A. Field of Invention
The present invention generally relates to exterior or interior illumination using architectural-system, often historical-style (hereafter sometimes referred to as “architectural and historical/architectural”) light fixtures such as street lamps mounted on decorative posts, wall-mounted lights, acorn-style fixtures and similar fixtures. The present invention specifically relates to lighting systems or fixtures that provide the following: (1) a visible surface or light source (e.g. luminous surface/transmissive surface/visible lamp) or other source of reference illumination and (2) controlled task or area illumination for one or more targeted areas.
B. Architectural and Historical/Architectural, and/or Functional Lighting for Site Indication, Location Reference, and Task Lighting
Architectural and historical/architectural fixtures as described above are used in many applications to provide a specific appearance, either as part of an overall theme or simply to provide aesthetic benefits to an area. Simplified examples of these types of fixtures are shown at FIGS. 1A-D. Of these types, the globe-style street lamp (FIG. 1A) and acorn-style street lamp (FIG. 1B) are very common. They can be supported/elevated on a variety of structures. Just a few examples for illustration are posts (FIGS. 1A and 1B) or wall brackets (FIGS. 1C and 1D). These fixtures have distinctive historical/architectural features, which are directly apparent both during daytime whether or not turned on and at night when turned on. They generally are intended to provide one or more benefits when used as illumination sources. First, they are intended to provide “site indicator/guide lighting” (hereafter “indicator lighting”) from a “visible luminous surface light source” (hereafter sometimes referred to as “luminous surface”) in order to provide a positive indication of designated areas, paths, or roadways. The distinctive architectural or historical style provides this indicator function during daylight hours. The style is similarly viewable when turned on at night, but the luminous aspects when turned on at night can also provide an indicator function. Second, they are most times intended to provide task lighting for targeted areas such as sidewalks, roads, or paths. That is, they are intended to provide some illumination of area around the light. Third, they can be intended to provide a source of reference illumination for nearby surfaces such as walls, doorways, and/or other visual surfaces in order to provide observers with a reference for location, distance, size, etc. The visible light source and illumination of the structure provide visible presence of the structure or features against its surroundings to persons in the area. However, fixtures such as FIGS. 1A-D have certain characteristics which leave room for improvement in the art, as will be discussed in more detail later.
The “lantern” style fixture of FIG. 1D uses frosted or clear glass in a similar fashion.
Another type of fixture that may be architectural, historical/architectural, or merely functional that is often used for nighttime illumination of structures is commonly known as a wall pack fixture (e.g. FIG. 1E). These fixtures are typically mounted to existing structures where electrical power is conveniently available. They can also provide indicator, task, and reference lighting. These fixtures also have certain deficiencies, which will also be outlined briefly below.
C. Light Distribution Pattern as a Deficiency of Architectural and Historic/Architectural Fixtures
The optical design of many architectural and historical/architectural lights (e.g. FIGS. 1A, 1B and 1C) is normally not well adapted to providing task lighting due to its inherent light distribution pattern. In general, these fixtures use an upwardly oriented lamp and distribute light nearly omni-directionally, with the exception that a lower supporting structure blocks light directed down from or near to the fixture. A relatively small amount of the light from the fixture is therefore able to reach the intended target. This will remain the case even if lamp brightness is increased in an attempt to overcome this deficiency. Additionally, much of the light is wasted by being directed upwardly.
D. ‘Scene Brightness Ratio’ as an Inherent Deficiency of Architectural, Historic/Architectural, and/or Functional Fixtures
Due to well-known optical principles, the effectiveness of the task lighting is unavoidably reduced when a single luminous surface (e.g. the globe of FIGS. 1A, 1B and 1C, the panes of FIG. 1D, and the lens of FIG. 1E) is used to provide both indicator lighting and task lighting on a target area. It is known in the art that when light from these types of fixtures is reflected from a surface (e.g. ground and/or sidewalk, path, or street and/or floor X, FIG. 1F), that reflected light will always have a lower luminance than the original source of the reflected light which originates from a luminous source (such as from an architectural or historic/architectural fixture 10, FIG. 1F), since the luminous source will always be smaller than the reflecting surface in these applications. It is also known in the art (as will be discussed below) that the eye adapts to the brightest source of luminance within its field of vision (which in this example of FIG. 1F tends to be the luminous surface of fixture 10 at night when it is turned on). Therefore the eye will be less sensitive to the light reflected from the target area in FIG. 1F (e.g. surface X) than it would be to the direct luminance from the luminous surface (e.g. fixture 10 in FIG. 1F). The result is less visibility of the target area X in FIG. 1F (at any given luminance value of the single luminous source 10) in comparison, for example, to the visibility of a target area (e.g. X, FIG. 1G) wherein there is no luminous source visible to the observer such as, for example, just a directional task light 11 (FIG. 1G) which has no direct luminance to the viewer because its light source is shielded from direct view and its light output is directional. Another way of stating this principle is that the greater the ‘scene brightness ratio’ (i.e. the ratio of the brightest source of luminance in the scene vs. the luminance from the target area), the less effective will be the target illumination. This issue exists likewise for known fixtures like FIGS. 1D and 1E.
Thus architectural and historic/architectural lighting fixtures, by inherent design, are limited from providing effective target area illumination, particularly in comparison with a lighting fixture with a non-visible source of target illumination. Such fixtures by design create a ‘scene brightness ratio’ that causes the eye to adapt to the luminance of the luminous surface, which therefore relatively diminishes the effectiveness of the task lighting it provides. As illustrated in FIG. 1F, if the viewer has direct view of luminous source 10 when luminous source 10 has greater brightness than surface X, there is less visibility of surface X. On the other hand, FIG. 1G illustrates higher visibility of surface X if it is brightest in field of view (here no direct view or luminance shown), but there is no guide lighting that would otherwise be provided by the luminous surface.
E. ‘Total Adaptive Range’and ‘Scene Adaptive Range’ of the Visual System
The ability of the human eye and visual system (hereafter “the eye”) to adapt automatically to various levels of light has two separate but related domains: (a) Overall, the eye has a very wide ‘total adaptive range’ which allows useful visual perception over a very wide range of luminance levels. These levels can vary by a factor of easily 250,000:1 (possibly much more in some individuals). For example, starlight can have a light level of 0.001 lux, moonlight may be 0.3 lux, and full sunlight may be up to 100,000 lux. (The ratio between sunlight and moonlight can be on the order of 300,000 to 1; between sunlight and starlight as much as 100,000,000 to 1). (b) In general, the eye has a ‘scene adaptive range’ within which the eye can effectively perceive objects without undergoing an adaptive change. This scene adaptive range can vary between individuals and between ambient light conditions. For lower light or nighttime conditions, it may be on the order of 10:1 or 20:1; for daytime conditions it may be significantly higher, on the order of 250:1 or more. For very low light conditions approaching the lowest level of the eye's sensitivity, it may be lower than 10:1.
For purposes of applications of use, according to many aspects of the present invention, it is most important to note that the scene adaptive range of the eye determines the effectiveness of task lighting in an area. If the scene adaptive range of the eye is 10:1 (for a given location and ambient light level), then the brightest point in the field of vision should not be more than ten times brighter than the target area. Thus if the ‘scene brightness ratio’ (see discussion above) is 100:1 when the scene adaptive range of the eye is 10:1, the effectiveness of the target illumination will diminish, and subjective perception of glare and veiling luminance may occur. Efforts to increase the effectiveness of the lighting of the target area will therefore be subject to the constraints of the scene adaptive range of the eye.
Therefore, if the primary light source (e.g. the luminous surface) is quite bright compared to outdoor surroundings at night, a low level of illumination on the target that would otherwise be acceptable becomes insufficient. The eye has adapted itself to a bright light source that, unfortunately, has most of its effect on the eye, and little effect in providing useful light that is illuminating the target area. Thus, although the measured light level is relatively high, the usefulness of the light is very low.
Thus, any given lighting fixture for which the effective scene brightness ratio is greater than the scene adaptive range of the eye will, by inherent design, automatically tend to obscure the target area and tend to create conditions of glare or veiling luminance. Thus, for a fixture with an effective scene brightness ratio that is greater than the scene adaptive range of the eye, attempting to improve the visual effectiveness of the target illumination cannot be accomplished by either increasing or decreasing the luminance of the fixture, since the fixture's effective scene brightness remains outside the usable range.
Conversely, a fixture with an effective scene brightness ratio that is within the scene adaptive range of the eye, as will be detailed according to certain aspects of the present invention, will tend to provide effective and pleasing illumination of the target area, and will tend to allow use in widely varying ambient conditions since it will be seen that increasing the target area luminance can still be done within the scene adaptive range of the eye.
F. ‘Glare’ as a Visual Phenomenon
Certain terms in common use describe, non-scientifically, the effects of lighting sources that exceed the ability of the eye to adapt (see discussion of eye adaptivity above). For instance, the term ‘glare’ loosely describes various undesirable effects resulting in reduced vision and unpleasant or painful observer experiences. Depending on the circumstances, glare may be categorized as ‘discomfort glare’, ‘distracting glare’, ‘disabling glare’, or ‘blinding glare’. (Other nomenclatures may be in use as well.) The term ‘veiling luminance’ is similarly used to describe a condition in which a source within the visual field of an observer is sufficiently bright such that other objects are visually obscured. Both effects are attempts to describe the visual effect of circumstances wherein the source of direct luminance is brighter than the surrounding field of vision in excess of the eye's ability to adapt.
Anecdotally, these conditions are well known to most people from the experience of driving on a 2-lane highway and meeting a vehicle with its headlights on high beam. Ambient conditions determine whether the glare and veiling luminance is perceived. If it is bright sunlight, the light from the headlights may be nearly imperceptible; under cloudy or twilight conditions, the light from the headlights is perceptible, but not distracting. However on a very dark night, the light from the headlights can be, for various people, uncomfortable, distracting, disabling, or even blinding. Thus the perceived brightness of the headlights, and any perception of glare or veiling luminance, occurs based on the source of glare being significantly brighter than the brightest source of light to which the eye was previously adapted.
G. ‘Design for Glare’ in Architectural and Historical/Architectural Fixtures
Because architectural and historical/architectural fixtures are intended to function as indicator lights—which by definition must be directly visible in the observer's field of view—these fixtures must radiate light almost omni-directionally. This tends to result in undesired visual effects (‘glare’) for the observer. For the observer in the target area who is experiencing the effects of glare, efforts to increase target area illumination by increasing the radiated light from the fixture tend to be counterproductive because it is recognized that (again, by design) these fixtures provide relatively poor target illumination and this does not change the ‘scene brightness ratio’ relative to the scene adaptive range of the observer's eye and therefore does not increase the effectiveness of the task lighting (and may in fact make the task lighting less effective relatively) but may increase the perception of glare.
For observers outside the target area, existing historical/architectural fixtures can also cause unintended negative effects. As previously noted, much of the light goes in directions other than the target. This ‘spill light’ contributes to well-known issues with light pollution in the immediate vicinity as well as contributing to societal concerns such as night sky glow and reduction of nighttime sky visibility.
For examples of standard industry references to these concepts, refer to IESNA ED-100, pp 2-14, 2-15 available from Illuminating Engineering Society of North America; CIE publication 112-1994 available from the International Commission of Illumination (CIE); and IESNA TM-11-00 available from Illuminating Engineering Society of North America; each incorporated by reference herein.
H. Efficiency of Architectural and Historical/Architectural Fixtures
Existing architectural and historical/architectural fixtures may be quite inefficient for several reasons: These fixtures typically use incandescent or high intensity discharge type lamps, ranging in power from 100 to 400 watts or more, and are physically of a size that would be difficult to include as a task light without disrupting the historical and/or architectural aesthetics of the light. Compared to other types of fixtures with the same power usage, only a small percentage of the light output is typically used to light the target area, due to the non-controlled nature of the illumination provided. In addition, glare from such fixtures reduces the effectiveness of the small amount of available illumination. Therefore, very high power levels relative to other types of fixtures can be required to provide (somewhat) effective illumination of the target area.
I. Cutoff Type Fixtures Ineffective as an Answer to Deficiencies in Architectural and Historical/Architectural Fixtures
As an answer to the aforementioned deficiencies in the art, “cutoff type fixtures” have been proposed as a solution. These types of fixtures are classified based on their effectiveness at controlling the amount of light radiated near horizontal (i.e. near 90° from nadir). Typical classifications range from (a) ‘semi-cutoff,’ which provides little means for limiting light intensity near horizontal, (b) ‘cutoff,’ which limits the light intensity at 80° from nadir to be 10% or less of rated lumens and which limits intensity at 90° to be 2.5% or less of the rated lumens, and (c) ‘full-cutoff,’ which limits the light intensity at 80° from nadir to be 10% or less of rated lumens and which limits light intensity at or above 90° from nadir to zero.
These types of fixtures generally do not adequately address the deficiencies in the art. First, there is usually a trade-off of historical/architectural character to achieve improved function. Second, these types of fixtures still allow some light at or near 90° from nadir (i.e. essentially, light still may travel horizontally), causing glare. Thus the eye's involuntary adaptive response can be triggered which reduces effectiveness of the illumination. (Examples of cut-off type fixtures and full-cutoff type fixtures are described and shown at www.lrc.rpi.edu/programs/nlpip/lightinganswers/lightpollution/lightPollution.asp and “Full Cutoff Lighting: The Benefits” at www.iesna.org. Third, the loss of the historical and architectural transmissive or luminous surface represented by the globe, acorn, panels, etc. causes a loss of the guide/indicator function during both daytime and nighttime hours.
J. Dark Sky Regulations
“Dark sky regulations/recommendations” are ordinances or industry standards which seek to reduce night sky glow, allowing better visibility of the nighttime sky and reducing the effects of unnatural lighting on the environment. An example of dark sky recommendations is found in the “Simple Guidelines for Lighting Regulations for Small Communities, Urban Neighborhoods, and Subdivisions” from the International Dark-Sky Association (http://www.darksky.org/mc/page.do?sitePageId=58881), incorporated by reference herein). The present invention proposes means to accommodate dark sky regulations/recommendations while preserving desired aesthetic qualities.
K. Color, Color Temperature, and Color Rendering Index (CRI)
Color, color temperature, and color rendering index (CRI) of lighting are all very complex subjects, but well-known to those skilled in the art. A limited discussion concerning the transmission and perception of color with reference to color temperature and CRI follows. First, visible light is a portion of the electromagnetic spectrum that can be perceived by the eye, generally considered to have a wavelength ranging from about 400 to 700 nm. Although the colors run as a continuum from shorter to longer wavelengths, ‘color’ as a physical phenomenon generally refers to a particular wavelength or range of wavelengths within the visible spectrum. One standard division of the spectrum is as follows: violet 400-450 nm, blue 450-490 nm, green 490-560 nm, yellow 560-590 nm, orange 590-630 nm, red 630-700 nm.
Light, such as sunlight, having a relatively even distribution of the wavelengths from 400-700 nm is perceived of as ‘white.’ White light may be described in terms of its ‘color temperature’, which is based on the distribution of wavelengths generated by a ‘black body radiator’ at a specific temperature on the Kelvin scale. A color temperature of 2800 K, such as emitted by an incandescent light bulb, while nominally ‘white’ has a reddish-yellow tinge. Typical daylight has a color temperature of 5500-6000 K. An overcast sky will typically have a color temperature around 6500 K. (Paradoxically, by convention, observer perception of ‘warmth’ or ‘coolness’ of the light is inverted with relationship to the actual temperature of the black body radiator. The light from an incandescent bulb at 2800 K is said to be ‘warmer’ than the physically much hotter overcast light at 6500 K which is described as “cool white.”).
Color Rendering Index (CRI) is a measurement of how colors are perceived by the eye when viewed under differing light sources. Incandescent light is given the standard value of 100 and other light sources are compared with their ability to render colors with the same observer perception, with higher (approaching 100) being ‘better’, at least by convention.
Architectural and historical/architectural fixtures which normally have a single light source can generate light of any particular color, color temperature, or CRI that is within the range of lamp technology, however as a single fixture they are limited to the rating of the lamp that is installed. Thus for aesthetic purposes, a low color temperature of 2800 K may be desired so that the transmissive or luminous surface looks ‘right’ for the scene. However, task lighting might render surroundings more effectively or pleasingly if a different color temperature could be used. Likewise, there could be reasons to vary color or CRI (or other characteristics not herein enumerated) of luminous surface lighting versus task lighting.
For example, a luminous surface biased towards a lower color temperature or redder color could provide a reference luminance that allows a relatively low eye adaptation response. At the same time, target illumination that is biased toward a higher color temperature or bluer color could provide improved effectiveness of target area illumination.
Thus, it is a deficiency of existing architectural and historical/architectural lights that they cannot ordinarily provide differing color temperatures, colors, or color temperatures, or other characteristics for the luminous surface and the task lighting. A fixture that can do so, as will be discussed below, would be a distinct improvement in the art.
As can be seen from the foregoing discussion, there is room for improvement in the art.